Generally, pneumatic tube transport systems convey materials between discrete points or stations. A carrier is positionable within a number of sealed tubes of the pneumatic tube transport system to transport products, documents, or other items. The carrier passes through the tubes by creating a zone of higher pressure air behind the carrier than exists in front of the carrier. A vacuum/zone of negative pressure in front of the carrier or a zone of positive pressure behind the carrier creates this pressure differential.
Accelerator rings or seal/wear bands on the carriers prevent excessive transfer (i.e., bypass) of air between the front of the carrier and the rear of the carrier. Seal/wear bands thus maintain the differential pressure between the front and rear portions of a carrier, which provides the force necessary to propel the carrier through the pneumatic tube system. Such seal bands typically engage the inner surface of the transport tube to support the carrier body and to inhibit air flow between the front and rear portions of the carrier. In this regard, it is important to minimize friction between the seal bands and the inner wall of the tube to enable the carrier to move through the tube without requiring high differential pressures between the front and rear of the carrier.
The size of the carrier and/or the intended payload of a carrier may affect the choice of materials for a seal/wear band. In this respect, soft, resilient materials, such as felt or cloth belting, may form wear bands for small diameter carriers transferring light loads. Such materials adapt closely to the inner surface of the transfer tube and are pliable enough to conform to surface irregularities within the tube. However, such materials do not provide sufficient load carrying capability when used with large diameter carriers designed for transferring heavy loads. Under such conditions, such materials may wear rapidly and/or crush, which may permit excessive air by-pass around the carrier.
Larger carriers or carriers designed to transport heavier payloads typically require a more rigid, wear resistant material to support their weight. For such applications, hard rubber or rubber reinforced leather belting sometimes form the seal/wear band. While such materials generally provide greater wear resistance, they are typically rigid and inflexible, and do not readily conform to surface irregularities (e.g., pipe junctions) within the transfer tube. Further, standard commercially available, metal or plastic tubes form most transfer tubes of pneumatic systems. Such tubes are available in various nominal sizes and are subject to manufacturing tolerances, which can vary the inner diameter of such tubes. Moreover, such tubes are generally not perfectly round. In this respect, most nominal sizes of tubing, especially metal tubing, have an ovality factor that is a dimension indicative of the degree or amount by which a cylindrical tube may be out-of-round. Accordingly, if a wear band is too rigid, it can cause the carrier to bind within the pneumatic tubes.